Photometric Estimates Research Articles

The structure of the stellar halo of the Andromeda galaxy explored with the NB515 for Subaru/HSC. I.: New insights on the stellar halo up to 120 kpc

Abstract We analyse the M31 halo and its substructure within a projected radius of 120 kpc using a combination of Subaru/HSC NB515 and CFHT/MegaCam g- & i-bands. We succeed in separating M31’s halo stars from foreground contamination with ∼ 90 % accuracy by using the surface gravity sensitive NB515 filter. Based on the selected M31 halo stars, we discover three new substructures, which associate with the Giant Southern Stream (GSS) based on their photometric metallicity estimates. We also produce the distance and photometric metallicity estimates for the known substructures. While these quantities for the GSS are reproduced in our study, we find that the North-Western stream shows a steeper distance gradient than found in an earlier study, suggesting that it is likely to have formed in an orbit closer to the Milky Way. For two streams in the eastern halo (Stream C and D), we identify distance gradients that had not been resolved. Finally, we investigate the global halo photometric metallicity distribution and surface brightness profile using the NB515-selected halo stars. We find that the surface brightness of the metal-poor and metal-rich halo populations, and the all population can be fitted to a power-law profile with an index of α = −1.65 ± 0.02, −2.82 ± 0.01, and −2.44 ± 0.01, respectively. In contrast to the relative smoothness of the halo profile, its photometric metallicity distribution appears to be spatially non-uniform with nonmonotonic trends with radius, suggesting that the halo population had insufficient time to dynamically homogenize the accreted populations.

Variational inference for acceleration of SN Ia photometric distance estimation with BayeSN

Abstract Type Ia supernovae (SNe Ia) are standarizable candles whose observed light curves can be used to infer their distances, which can in turn be used in cosmological analyses. As the quantity of observed SNe Ia grows with current and upcoming surveys, increasingly scalable analyses are necessary to take full advantage of these new datasets for precise estimation of cosmological parameters. Bayesian inference methods enable fitting SN Ia light curves with robust uncertainty quantification, but traditional posterior sampling using Markov Chain Monte Carlo (MCMC) is computationally expensive. We present an implementation of variational inference (VI) to accelerate the fitting of SN Ia light curves using the BayeSN hierarchical Bayesian model for time-varying SN Ia spectral energy distributions (SEDs). We demonstrate and evaluate its performance on both simulated light curves and data from the Foundation Supernova Survey with two different forms of surrogate posterior – a multivariate normal and a custom multivariate zero-lower-truncated normal distribution – and compare them with the Laplace Approximation and full MCMC analysis. To validate of our variational approximation, we calculate the pareto-smoothed importance sampling (PSIS) diagnostic, and perform variational simulation-based calibration (VSBC). The VI approximation achieves similar results to MCMC but with an order-of-magnitude speedup for the inference of the photometric distance moduli. Overall, we show that VI is a promising method for scalable parameter inference that enables analysis of larger datasets for precision cosmology.

Photometric redshifts probability density estimation from recurrent neural networks in the DECam local volume exploration survey data release 2

Photometric wide-field surveys are imaging the sky in unprecedented detail. These surveys face a significant challenge in efficiently estimating galactic photometric redshifts while accurately quantifying associated uncertainties. In this work, we address this challenge by exploring the estimation of Probability Density Functions (PDFs) for the photometric redshifts of galaxies across a vast area of 17,000 square degrees, encompassing objects with a median 5σ point-source depth of g= 24.3, r=23.9, i= 23.5, and z= 22.8 mag. Our approach uses deep learning, specifically integrating a Recurrent Neural Network architecture with a Mixture Density Network, to leverage magnitudes and colors as input features for constructing photometric redshift PDFs across the whole DECam Local Volume Exploration (DELVE) survey sky footprint. Subsequently, we rigorously evaluate the reliability and robustness of our estimation methodology, gauging its performance against other well-established machine learning methods to ensure the quality of our redshift estimations. Our best results constrain photometric redshifts with the bias of −0.0013, a scatter of 0.0293, and an outlier fraction of 5.1%. These point estimates are accompanied by well-calibrated PDFs evaluated using diagnostic tools such as Probability Integral Transform and Odds distribution. We also address the problem of the accessibility of PDFs in terms of disk space storage and the time demand required to generate their corresponding parameters.We present a novel Autoencoder model that reduces the size of PDF parameter arrays to one-sixth of their original length, significantly decreasing the time required for PDF generation to one-eighth of the time needed when generating PDFs directly from the magnitudes.

The Pristine survey. XXIV. The Galactic underdogs: Dynamic tales of a Milky Way metal-poor population

Metal-poor stars hold key information on the early Milky Way. Through the identification and characterisation of substructures, one can understand internal mechanisms (including merger and accretion events), which are indispensable to reconstruct the formation history of the Galaxy. To allow an investigation of a population of very metal-poor stars ( Fe/H < -1.7) with disc-like orbits (planar and prograde), high angular momenta ($L_z$/$J_ tot $ > 0.5) and rotational velocities ($V_ $) proposed in the literature, we used a sample of sim 3M giant stars with Gaia DR3 BP/RP information and Pristine-Gaia metallicities down to -4.0 dex that we aimed to decontaminate. To achieve this, we constructed a sample as free as possible from spurious photometric estimates, an issue commonly encountered for high $V_ metal-poor stars. We created a statistically robust sample of sim 36 000 Pristine-Gaia very metal-poor ( Fe/H < -1.7) giant stars, using APOGEE and LAMOST data (adding GALAH and GSP-spec for verification) to estimate and remove contamination. We investigated the spatial and kinematic properties of the decontaminated sample, making use of $V_ as well as the action space, which are both powerful tools to disentangle stellar populations. The global distribution of very metal-poor stars in our sample shows the typical kinematics, orbital properties, and spatial distributions of a halo; however, as in previous works, we found a pronounced asymmetry in the $L_z$ and $V_ distributions, in favour of prograde stars. We showed that this excess is predominantly due to prograde-planar stars (10 $<!PCT!>$ of the very metal-poor population), which can be detected down to Fe/H = -2.9 at a 2sigma confidence level. This prograde-planar population contains stars with $V_ $ and $Z_ max $ < 1.5\,kpc. While the overall orbital configurations max $ - $R_ max $ or action space distributions) of our sample match that of a halo, the highly prograde and planar subset (2 $<!PCT!>$ of the very metal-poor population) also bears characteristics classically associated with a thick disc: (i) a spatial distribution compatible with a short-scaled thick disc, (ii) a $Z_ max $ - $R_ max $ distribution similar to the one expected from the thick disc prediction of the Gaia Universe Model Snapshot, and (iii) a challenge to erase its signature assuming a stationary or prograde halo with $ V_ phi $ sim 30-40 km.s$^ $. Altogether, these results seem to rule out that these highly prograde and planar stars are part of a thin disc population and, instead, support a contribution from a metal-weak thick disc. Higher resolution spectra are needed to fully disentangle the origin(s) of the population.

Variation of the stellar initial mass function in semi-analytical models

Context. In our previous work, we derived the CR-IGIMF, which is a new scenario for a variable stellar initial mass function (IMF) that combines numerical results on the role played by cosmic rays (CR) in setting the thermal state of star-forming gas with the analytical approach of the integrated galaxy-wide IMF (IGIMF). Aims. In this work, we study the implications of this scenario for the properties of local early-type galaxies (ETG) as inferred from dynamical, photometric, and spectroscopic studies. Methods. We implemented a library of CR-IGIMF shapes in the framework of the galaxy evolution and assembly (GAEA) model. GAEA provides predictions for the physical and photometric properties of model galaxies and for their chemical composition. Our realization includes a self-consistent derivation of the synthetic spectral energy distribution for each model galaxy, which allows a direct derivation of the mass fraction in the mean IMF of low-mass stars (i.e., the dwarf-to-giant ratio, fdg) and a comparison with IMF-sensitive spectral features. Results. The predictions of the GAEA model implementing the CR-IGIMF confirm our previous findings: It correctly reproduces both the observed excess of z ∼ 0 dynamical mass (mass-to-light ratio) with respect to spectroscopic (photometric) estimates assuming a universal MW-like IMF, and the observed increase in [α/Fe] ratios with stellar mass in spheroidal galaxies. Moreover, this realization reproduces the increasing trends of fdg and IMF-sensitive line strengths with velocity dispersion, although the predicted relations are significantly shallower than the observed ones. Conclusions. Our results show that the CR-IGIMF is a promising scenario that reproduces at the same time dynamical, photometric, and spectroscopic indications of a varying IMF in local ETGs. The shallow relations found for spectral indices suggest that either a stronger variability as a function of galaxy properties or additional dependences (e.g., as a function of star forming gas metallicity) might be required to match the strength of the observed trends.

Metal-poor stars with disc-like orbits

We used photometric metallicity estimates for about 700 000 stars in the surroundings of the Sun, with very accurate distances and 3D motions measures from Gaia DR3, to explore the properties of the metal-poor (−2.0 < [Fe/H] ≤ −1.5; MP) and very metal-poor ([Fe/H] ≤ −2.0; VMP) stars with disc kinematics in the sample. We confirm the presence of a significant fraction of MP and VMP stars with disc-like orbits and that prograde orbits are prevalent among them, with a prograde-to-retrograde ratio of P/R ∼ 3. We highlight a statistically significant difference in the distribution of the Z component of the angular momentum (LZ) and orbital eccentricity between prograde and retrograde disc-like MP stars for the first time. The same kind of difference is found in the VMP sub-sample, albeit at a much lower level of statistical significance, likely due to the small sample size. We show that prograde disc-like MP and VMP stars display an additional component of the |LZ| distribution with respect to their retrograde counterpart. This component is at higher |LZ| with respect to the main peak of the distribution, possibly hinting at the presence of a pristine prograde disc in the Milky Way. This hypothesis is supported by the results of the analysis of a large sub-sample dominated by stars born in situ. In this case, the prevalence of prograde stars is also clearly detected at [Fe/H] ≤ −1.5, and their |LZ| distribution is more skewed toward high |LZ| values than their retrograde counterpart. This suggests that the seed of what will eventually evolve into the main disc components of the Milky Way may have already been in place in the earliest phases of the Galaxy assembly.

Unraveling the Origins and Development of the Galactic Disk through Metal-Poor Stars

The Milky Way is a spiral galaxy comprising three main components: the Bulge, the Disk, and the Halo. Of particular interest is the Galactic disk, which holds a significant portion of the baryonic matter angular momentum and harbors at least two primary stellar populations: the thin and thick disks. Understanding the formation and evolution of the Galactic disk is crucial for comprehending the origins and development of our Galaxy. Stellar archaeology offers a means to probe the disk’s evolution by listening to the cosmological narratives of its oldest and most pristine stars, specifically the metal-poor stars. In this study, we employed accurate photometric metallicity estimates and Gaia Early Data Release 3 astrometry to curate a pure sample of the oldest Galactic stars. This proceeding presents a summary of our primary findings.

Pure Spectroscopic Constraints on UV Luminosity Functions and Cosmic Star Formation History from 25 Galaxies at z spec = 8.61–13.20 Confirmed with JWST/NIRSpec

We present pure spectroscopic constraints on the UV luminosity functions and cosmic star formation rate (SFR) densities from 25 galaxies at z spec = 8.61–13.20. By reducing the JWST/NIRSpec spectra taken in multiple programs of Early Release Observation, Early Release Science, General Observer, and Director’s Discretionary Time observations with our analysis technique, we independently confirm 16 galaxies at z spec = 8.61–11.40, including new redshift determinations, and a bright interloper at z spec = 4.91 that was claimed as a photometric candidate at z ∼ 16. In conjunction with nine galaxies at redshifts up to z spec = 13.20 in the literature, we make a sample of 25 spectroscopically confirmed galaxies in total and carefully derive the best estimates and lower limits of the UV luminosity functions. These UV luminosity function constraints are consistent with the previous photometric estimates within the uncertainties and indicate mild redshift evolution toward z ∼ 12, showing tensions with some theoretical models of rapid evolution. With these spectroscopic constraints, we obtain firm lower limits of the cosmic SFR densities and spectroscopically confirm a high SFR density at z ∼ 12 beyond the constant star formation efficiency models, which supports earlier claims from the photometric studies. While there are no spectroscopically confirmed galaxies with very large stellar masses violating the ΛCDM model due to the removal of the bright interloper, we confirm star-forming galaxies at z spec = 11–13 with stellar masses much higher than model predictions. Our results indicate possibilities of high star formation efficiency (>5%), a hidden active galactic nucleus, a top-heavy initial mass function (possibly with Population III), and large scatter/variance. Having these successful and unsuccessful spectroscopy results, we suggest observational strategies for efficiently removing low-redshift interlopers for future JWST programs.

Reconsidering photometric estimation of local star formation environment and its correlation with Type Ia supernova luminosity

ABSTRACT Recent studies on the environmental dependence of Type Ia supernova (SN Ia) luminosity focus on the local environment where the SN exploded, considering that this is more directly linked to the SN progenitors. However, there is a debate about the local environmental, specifically local star formation rate (SFR), dependence of the SN Ia luminosity. A recent study claims that the dependence is insignificant (0.051 ± 0.020 mag; 2.6σ), based on the local SFR measurement by fitting local ugrizy photometry data. However, we find that this photometric local SFR measurement is inaccurate. We argue this based on the theoretical background of SFR measurement and the methodology used to make that claim with their local ugrizy photometry data, especially due to a limited range of extinction parameters used when fitting the data. Therefore, we reanalyse the same host galaxies with the same fitting code, but with more physically motivated extinction treatments and global ugriz photometry of host galaxies. We estimate global stellar mass and SFR. Then, local star formation environments are inferred by using the method which showed that SNe Ia in globally passive galaxies have locally passive environments, while those in globally star-forming low-mass galaxies have locally star-forming environments. We find that there is significant local environmental dependence of SN Ia luminosities: SNe Ia in locally star-forming environments are 0.072 ± 0.021 mag (3.4σ) fainter than those in locally passive environments, even though SN Ia luminosities have been further corrected by the BEAMS with Bias Corrections method that reduces the size of the dependence.

Beyond Spectroscopy. II. Stellar Parameters for over 20 Million Stars in the Northern Sky from SAGES DR1 and Gaia DR3

We present precise photometric estimates of stellar parameters, including effective temperature, metallicity, luminosity classification, distance, and stellar age, for nearly 26 million stars using the methodology developed in the first paper of this series, based on the stellar colors from the Stellar Abundances and Galactic Evolution Survey (SAGES) Data Release 1 and Gaia Early Data Release 3. The optimal design of stellar-parameter sensitive uv filters by SAGES has enabled us to determine photometric-metallicity estimates down to −3.5, similar to our previous results with the SkyMapper Southern Survey (SMSS), yielding a large sample of over five million metal-poor ([Fe/H] ≤ −1.0) stars and nearly one million very metal-poor ([Fe/H] ≤ −2.0) stars. The typical precision is around 0.1 dex for both dwarf and giant stars with [Fe/H] > −1.0, and 0.15–0.25/0.3–0.4 dex for dwarf/giant stars with [Fe/H] < −1.0. Using the precise parallax measurements and stellar colors from Gaia, effective temperature, luminosity classification, distance, and stellar age are further derived for our sample stars. This huge data set in the Northern sky from SAGES, together with similar data in the Southern sky from SMSS, will greatly advance our understanding of the Milky Way, in particular its formation and evolution.

Spectroscopic searches for evolutionary orbital period changes in WR+OB binaries: the case of V444 Cyg

ABSTRACT We present the results of new photometric and spectroscopic observations of the WN5+O6 binary V444 Cyg and a detailed analysis of extant spectroscopy and photometry. Using elements of the spectroscopic orbit and assuming e ≈ 0, i ≈ 78° we determined the masses and orbit sizes of the components of V444 Cyg as MO6 ≈ 26.4 M⊙, MWN5 ≈ 10.7 M⊙, aO6 ≈ 10.6 R⊙, aWN5 ≈ 26.1 R⊙. Based on new and archival light curves and using the Hertzsprung method, we improved the photometric estimate of the secular increase rate of the orbital period in V444 Cyg, obtaining $\dot{P}_{\mathrm{ph}} = 0.119\pm 0.003$ s yr−1. From a comparison of the new and archival radial velocity curves of V444 Cyg, we independently derived the secular orbital period change rate as $\dot{P}_{\mathrm{sp}} = 0.147\pm 0.032$ s yr−1, in agreement with the photometric $\dot{P}_{\mathrm{ph}}$. The obtained secular increase rate of the binary orbital period $\dot{P}$ and the mean radii of the components enabled us to estimate the stellar wind mass-loss rate from the WR star as $\dot{M}_{\mathrm{WN5}} = -(6.0\pm 0.4)\times 10^{-6}~{\rm M}_{\odot }\mbox{ yr}^{-1}$.

UNCOVER: The Growth of the First Massive Black Holes from JWST/NIRSpec—Spectroscopic Redshift Confirmation of an X-Ray Luminous AGN at z = 10.1

The James Webb Space Telescope is now detecting early black holes (BHs) as they transition from “seeds” to supermassive BHs. Recently, Bogdan et al. reported the detection of an X-ray luminous supermassive BH, UHZ-1, with a photometric redshift at z > 10. Such an extreme source at this very high redshift provides new insights on seeding and growth models for BHs given the short time available for formation and growth. Harnessing the exquisite sensitivity of JWST/NIRSpec, here we report the spectroscopic confirmation of UHZ-1 at z = 10.073 ± 0.002. We find that the NIRSpec/Prism spectrum is typical of recently discovered z ≈ 10 galaxies, characterized primarily by star formation features. We see no clear evidence of the powerful X-ray source in the rest-frame UV/optical spectrum, which may suggest heavy obscuration of the central BH, in line with the Compton-thick column density measured in the X-rays. We perform a stellar population fit simultaneously to the new NIRSpec spectroscopy and previously available photometry. The fit yields a stellar-mass estimate for the host galaxy that is significantly better constrained than prior photometric estimates ( M ⊙). Given the predicted BH mass (M BH ∼ 107–108 M ⊙), the resulting ratio of M BH/M ⋆ remains 2 to 3 orders of magnitude higher than local values, thus lending support to the heavy seeding channel for the formation of supermassive BHs within the first billion years of cosmic evolution.

Photometric metallicities of fundamental-mode RR Lyr stars from Gaia G band photometry of globular-cluster variables

ABSTRACT Photometric metallicity formulae of fundamental-mode RR Lyr (RRab) stars are presented using globular-cluster data exclusively. The aim is to check whether this selection may help increasing the overall accuracy of the fits and eliminating the systematic bias of the photometric results, namely that they tend to overestimate [Fe/H] of the most metal-poor variables. The G band time-series data available in the Gaia DR3 archive and a new compilation of the published spectroscopic globular cluster [Fe/H] values on a uniform solar reference metallicity scale are utilized. We have derived a new [Fe/H]phot − P, φ31 formula, and have diagnosed that no significant increase in the accuracy of the fit can be achieved using non-linear or multiparameter formulae. The best result is obtained when different formulae are applied for variables with Oosterhoff (Oo)-type I and II properties. However, even this solution cannot eliminate the systematic bias of the results completely. This separation of the variables has also led to the conclusion that the photometric estimates of the [Fe/H] are less reliable for the Oo-type II variables than for the Oo-type I sample. Published [Fe/H]phot values and the results of the available photometric formulae in the Gaia G band are compared with the present results. It is found that each of the solutions yields very similar results, with similar accuracy and systematic biases. Major differences are detected only in the zero-points of the [Fe/H] scales, and these offsets are larger than differences in the accepted solar reference values would explain.

Correction to: Photometric mass estimation and the stellar mass–halo mass relation for low mass galaxies

Correction to: Photometric mass estimation and the stellar mass–halo mass relation for low mass galaxies

Euclid preparation

The European Space Agency's Euclid mission will provide high-quality imaging for about 1.5 billion galaxies. A software pipeline to automatically process and analyse such a huge amount of data in real time is being developed by the Science Ground Segment of the Euclid Consortium; this pipeline will include a model-fitting algorithm, which will provide photometric and morphological estimates of paramount importance for the core science goals of the mission and for legacy science. The Euclid Morphology Challenge is a comparative investigation of the performance of five model-fitting software packages on simulated Euclid data, aimed at providing the baseline to identify the best-suited algorithm to be implemented in the pipeline. In this paper we describe the simulated dataset, and we discuss the photometry results. A companion paper is focussed on the structural and morphological estimates. We created mock Euclid images simulating five fields of view of 0.48 deg2 each in the IE band of the VIS instrument, containing a total of about one and a half million galaxies (of which 350 000 have a nominal signal-to-noise ratio above 5), each with three realisations of galaxy profiles (single and double Sérsic, and 'realistic' profiles obtained with a neural network); for one of the fields in the double Sérsic realisation, we also simulated images for the three near-infrared YE, JE, and HE bands of the NISP-P instrument, and five Rubin/LSST optical complementary bands (u, g, r, i, and z), which together form a typical dataset for an Euclid observation. The images were simulated at the expected Euclid Wide Survey depths. To analyse the results, we created diagnostic plots and defined metrics to take into account the completeness of the provided catalogues, as well as the median biases, dispersions, and outlier fractions of their measured flux distributions. Five model-fitting software packages (DeepLeGATo, Galapagos-2, Morfometryka, ProFit, and SourceXtractor++) were compared, all typically providing good results. Of the differences among them, some were at least partly due to the distinct strategies adopted to perform the measurements. In the best-case scenario, the median bias of the measured fluxes in the analytical profile realisations is below 1% at a signal-to-noise ratio above 5 in IE, and above 10 in all the other bands; the dispersion of the distribution is typically comparable to the theoretically expected one, with a small fraction of catastrophic outliers. However, we can expect that real observations will prove to be more demanding, since the results were found to be less accurate for the most realistic realisation. We conclude that existing model-fitting software can provide accurate photometric measurements on Euclid datasets. The results of the challenge are fully available and reproducible through an online plotting tool.

Study of the open clusters in Kepler prime field

ABSTRACTWe present a detailed study of NGC 6791, NGC 6811, NGC 6819, and NGC 6866, the four open clusters that are located in the Kepler prime field. We use new CCD UBV(RI)KC photometry, which was combined with Gaia EDR3 photometric/astrometric data, to derive the astrophysical parameters with two-independent methods – one of them the fitCMD algorithm. Furthermore, we provide among others estimates of the mass and mass function, the cluster structure, derive the cluster orbits, and discuss the cluster dynamics. All objects belong to the older open cluster population (∼1–7 Gyr), are in an advanced dynamical stage with signs of mass segregation, and are located close to the solar circle, but show a large range in respect of radii, member stars or observed cluster mass ($\sim 100\!-\!2000\, \mathrm{M}_\odot$). For the three younger objects, we were also able to provide photometric metallicity estimates, which confirms their status as clusters with a roughly solar metallicity. The most outstanding object is clearly NGC 6791, a very old cluster with a high metallicity at a distance of about 4.5 kpc from the Sun. We estimate a probable radial migration by about 7 kpc, resulting in a birth position close to the Galactic centre.

Photometric Metallicity and Distance Estimates for ∼136,000 RR Lyrae Stars from Gaia Data Release 3

We present a sample of 135,873 RR Lyrae stars (RRLs) with precise photometric metallicity and distance estimates from our newly calibrated P–ϕ 31–R 21–[Fe/H]/P–R 21–[Fe/H] and G-band absolute magnitude–metallicity relations. The P–ϕ 31–R 21–[Fe/H] and P–R 21–[Fe/H] relations for type RRab and type RRc stars are obtained from nearly 2700 Gaia-identified RRLs, with precise ϕ 31 and R 21 measurements from light curves and metallicity estimates from spectroscopy. Using a few hundreds of nearby RRLs, with accurate distances estimated from the parallax measurements in Gaia Early Data Release 3, new G-band absolute magnitude–metallicity relations and near-IR period–absolute magnitude–metallicity relations are constructed. External checks, using other high-resolution spectroscopic samples of field RRLs and RRL members of globular clusters, show that the typical uncertainties in our photometric metallicity estimates are about 0.24 and 0.16 dex for type RRab and type RRc stars, respectively, without significant systematic bias with respect to the high-resolution spectroscopic metallicity measurements. The accuracies of these metallicity estimates are much improved, especially for type RRab stars, when compared to those provided by Gaia Data Release 3. Validations of our distance estimates, again using members of globular clusters, show that the typical distance errors are only 3%–4%. The distance moduli μ 0 = 18.503 ± 0.001 (stat) ± 0.040 (syst) mag for the Large Magellanic Cloud (LMC) and μ 0 = 19.030 ± 0.003 (stat) ± 0.043 (syst) mag for the Small Magellanic Cloud (SMC) are estimated from our type RRab star sample and are in excellent agreement with previous measurements. The mean metallicities of the LMC and SMC derived in this work are also consistent with previous determinations. Using our sample, a steep metallicity gradient of −0.024 ± 0.001 dex kpc−1 is found for the LMC, while a negligible metallicity gradient is obtained for the SMC.

Three Ultra-short-period Contact Eclipsing Binary Systems Mined from Massive Astronomical Surveys

We present the photometric analysis of three ultra-short-period total eclipsing binaries in contact configuration, CRTS_J172718.0+431624, OGLE-BLG-ECL-000104, and OGLE-BLG-ECL-000012, mined from massive astronomical surveys. Using the available archival light curves (LCs) from Vista Variables in the Vía Láctea (VVV), Optical Gravitational Lensing Experiment (OGLE), Zwicky Transient Facility, and Catalina Sky Survey in different passbands and new multiband photometric observations with the 2.3 m Aristarchos telescope at Helmos Observatory, their relative physical parameters were derived. We explored the parameter space by using the PIKAIA genetic algorithm optimizer. The best photometric solution and error budget estimation were adopted for each system through Markov Chain Monte Carlo sampling of the global optimum. The approximate absolute parameters were derived for each contact system adopting an empirical mass–luminosity relation. All three systems have a mass ratio lower than 0.5. The exchange between the primary and secondary depths of CRTS_J172718.0+431624 during 2016–2022 may be due to spot activity. In addition, we present a detailed analysis of the first well-characterized shortest-period contact eclipsing binary with total eclipses known so far (OGLE-BLG-ECL-000104). Thanks to VVV and OGLE LCs, new distances were derived for OGLE-BLG-ECL-000104 and OGLE-BLG-ECL-000012 using empirical period–luminosity relations. The origin and evolutionary status of all three ultra-short-period contact binaries are thoroughly discussed in the context of the detached binary formation channel.

Photometric Calibrations of M-dwarf Metallicity with Markov Chain Monte Carlo and Bayesian Inference

Knowledge of stellar atmospheric parameters (T eff, , [Fe/H]) of M dwarfs can be used to constrain both theoretical stellar models and Galactic chemical evolutionary models, and guide exoplanet searches, but their determination is difficult due to the complexity of the spectra of their cool atmospheres. In our ongoing effort to characterize M dwarfs, and in particular their chemical composition, we carried out multiband photometric calibrations of metallicity for early- and intermediate-type M dwarfs. The third Gaia data release provides high-precision astrometry and three-band photometry. This information, combined with the 2MASS and CatWISE2020 infrared photometric surveys and a sample of 4919 M dwarfs with metallicity values determined with high-resolution spectroscopy by The Cannon and APOGEE spectra, allowed us to study the effect of the metallicity in color–color and color–magnitude diagrams. We divided this sample into two subsamples: we used 1000 stars to train the calibrations with Bayesian statistics and Markov Chain Monte Carlo techniques, and the remaining 3919 stars to check the accuracy of the estimations. We derived several photometric calibrations of metallicity applicable to M dwarfs in the range of −0.45 ≤ [Fe/H] ≤ + 0.45 dex and spectral types down to M5.0 V that yield uncertainties down to the 0.10 dex level. Lastly, we compared our results with other photometric estimations published in the literature for an additional sample of 46 M dwarfs in wide binary systems with FGK-type primary stars and found a great predictive performance.

Redder than Red: Discovery of an Exceptionally Red L/T Transition Dwarf

We present the discovery of CWISE J050626.96+073842.4 (CWISE J0506+0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a (J − K)MKO color of 2.97 ± 0.03 mag and a J MKO − W2 color of 4.93 ± 0.02 mag, making CWISE J0506+0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506+0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity, late-type L/T transition dwarf. The spectrum of CWISE J0506+0738 shows possible signatures of CH4 absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8γ–T0γ. We tentatively find that CWISE J0506+0738 is variable at 3–5 μm based on multiepoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in the β Pic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.